The concept of smart grid, which is a highly intellectual power network, has been spreading. Correspondingly, various dispersed power sources are actively employed when generating power by using renewable energy such as solar power, wind power, and hydraulic power, and storage batteries are used as buffers to stabilize the power. It is considered that the relation between the power supply/demand system and customers will be more complicated.
As a conventional charge management method, there is known a method for keeping electric cost low by managing the storage battery so that the storage battery is preferably charged in the time period such as the nighttime etc. (recommended feeding time) when power cost is inexpensive. Further, in a lithium-ion storage battery currently used widely as a storage battery, it is generally said that its capacity performance deteriorates when the battery is kept in a full charge state, and that its lifetime is shortened when the battery is recharged after being completely discharged compared to the case of normal use. Therefore, the lithium-ion storage battery is required to be in a charge state between 20% and 80% to restrain the deterioration in its capacity performance.
The conventional technique intends to optimize charge/discharge only in terms of power cost, considering economic efficiency when storing power in a storage battery. In the conventional technique, environmental load when charging the storage battery and deterioration in the storage battery are not considered.